$2 THE BIOLOGY OF THE FROG chap. 



that in young frogs it is often very difficult to distinguish 

 the sexes. The gonads of the males frequently contain 

 numerous egg follicles and have the general appearance of 

 ovaries, and many frogs which would naturally be taken for 

 females show only male characters at a later period of devel- 

 opment. Estimates based on the appearance of the sex 

 organs of frogs during the first year of their life gave a very 

 large percentage of females. This percentage was found to 

 vary greatly in lots of frogs taken at different localities. 

 The degree of development of the sex organs does not 

 closely correspond with the development of the other parts 

 of the body, and there is consequently a great variation in 

 the appearance of these organs in specimens of the same 

 age. As there is no evidence that the mortahty of the 

 young females greatly exceeds that of the young males, and 

 as the proportion of the adults of the two sexes is nearly the 

 same, it is probable that many of the young frogs which 

 would ordinarily be diagnosed as females are ''juvenile 

 hermaphrodites " in which the female characters predomi- 

 nate for a time but which later develop into males. This 

 conclusion is supported by the fact that there are many 

 cases in which the sex glands are intermediate in appearance 

 between ovaries and testes. Egg follicles are often found in 

 the testes of frogs at a later period of development. 



Copulation in Late Summer. — Fischer-Sigwart has ob- 

 served that in July and August the sexual instinct of the 

 males kept in terraria often asserts itself a second time, 

 especially if they have been well fed and are in good condi- 

 tion. No sexual products are extruded at this time from 

 either sex, although the males show a strong proclivity to 

 clasp the female and will even clasp other males. A case is 

 related of a male who observed a female which had seized 

 an earthworm, and in attempting to share the morsel clam- 



